This invention relates generally to electrical power supply wiring used in commercial refrigeration and more particularly to a wiring system for a line-up of refrigerated merchandisers.
Commercial refrigeration systems are most commonly used, for example, to provide the large refrigeration requirements for a supermarket. In the supermarket example, food is displayed in merchandisers located around the shopping arena of the food store. The merchandisers are generally arranged in line-ups of two or more in which the merchandisers are oriented end-to-end. Most often the in-line merchandisers refrigerate food in the same temperature range, for example, low temperature refrigeration of frozen foods and ice cream at the product temperatures in the range of -20.degree. F. to 0.degree. F., or normal temperature refrigeration of fresh foods including meat, dairy and produce at product temperatures in the range of 28.degree. F. to 50.degree. F. The merchandisers in the same line-up are serviced by a single condensing unit, typically comprising plural multiplexed compressors and a condenser for refrigeration in the particular range. The condensing unit is piped to evaporators in each of the merchandisers in the line-up to achieve the desired refrigeration. It is also known to refrigerate product zones in a merchandiser by absorption refrigeration in which there is no change of phase of the cooling medium in the heat exchanger in the product zone, including secondary coolant systems such as the so-called "glycol-type" system.
The merchandisers have a number of electrical components, including lights, fans, case controllers, solenoid valves, anti-condensate heaters and electric defrost. Not all of the foregoing components will be on every case (for instance, if hot gas or off time is used for defrost), but all cases will have multiple electrical components and there may be still other electrical components provided in the merchandiser.
Installation of the line-up of merchandisers, particularly in a new supermarket, involves not only piping each merchandiser to the condensing unit, but also wiring the merchandisers to a source of electrical power. Presently electrical wiring of merchandisers is complex and time consuming, adding significantly to the time it takes to install the merchandisers and sometimes delaying opening of the supermarket. Electrical wiring is subject to code regulation under the National Electrical Code (NEC), and also to local building codes. Each merchandiser has a data plate describing the electrical requirements of the merchandiser. The data plate will include, for example, values for lights, fan motors, anti-condensate heaters and defrost heaters. A marking for the fan circuit maximum overcurrent protection device will also appear on the plate. Article 422 of the NEC requires all appliances (e.g., a merchandiser) be installed according to the ratings listed on their individual data plates.
A merchandiser, such as a reach-in refrigerator with five doors, will have a 120 volt lighting circuit of 3.2 amperes, a 120 volt fan circuit (including condensate heaters) of 13.5 amperes and a 208 volt defrost circuit of 22.8 amperes. The fan circuit will be limited to no greater than a 20 ampere overcurrent protection device. The lighting circuit is most often made up of fluorescent lamps which are also required to have overcurrent protection of no greater than 20 amperes. The NEC limits the defrost circuit to 1.25 times the defrost amperage (i.e., 28.5 amperes). A typical configuration would be to place three of these merchandisers in a line-up in the supermarket for holding frozen foods and ice cream.
Power for merchandisers in the supermarket is supplied from a circuit breaker box located in a service area or back room, outside the shopping arena of the supermarket. In the example of the low temperature reach-in refrigerators mentioned above, numerous electrical circuits extending from the circuit breaker box to each merchandiser in the line-up would have to be wired. There would be three 30 ampere, 208 volt circuits for the electric defrost (i.e., one circuit for each merchandiser), three 120 volt circuits for the fans/anti-condensate heaters and one 120 volt circuit for the lights of the three merchandisers. Thus, at least seven separate electrical circuits must be brought out to the line-up in this example. When multiplied over the entire supermarket, it is seen that large numbers of wires are present and a large number of hard wire connections must be made by an electrician to complete installation.
The complexity of wiring the power to the merchandisers is further increased by the desire to balance the load as much as possible among the three phases of electrical power which are provided. Frequently, none of the electrical components in the merchandisers require more than single phase power. However, when the merchandisers have electric defrost two phases are wired to the defrost. If all or a substantial majority of the merchandisers are wired to the same phase, there is an unbalance of load among the phases which should be avoided. It is known to balance the load by wiring each case in a line-up to a separate phase. However, because the wiring is done by hard wire connections it is very difficult to keep track of which merchandiser has been wired to which phase. Thus, wiring electrical power to multiple in-line merchandisers is time consuming and complicated.